Petroleum refining with organic acid anhydrides



United States Patent ABSTRACT OF THE DISCLOSURE A process for treatingpetroleum stocks to improve their storage stability by successiveadmixture with the stock of first, an organic acid anhydride, andsecond, sodium methylate in an amount sufficient to neutralize theadmixture.

This invention relates to the refining of petroleum, and moreparticularly to the chemical refining of petroleum including both crudepetroleum and the fractions produced therefrom in the course ofprocessing the crude petroleum.

Most crude petroleums include sulfur compound-s, phenolic andnitrogenous bodies, acids and the like which impart t0 the variousfractions produced in the processing of the crude petroleum undesirablephysical and chemical characteristics. These undesirable characteristicsinclude bad odor, sourness to the conventional *doctor" test, poor colorstability in storage formation of gummy precipitates in storage which,in the case of household fuel oils, are particularly deleterious. In thecase of gasoline fractions, these undesirable constituents alsofrequently reduce the clear octane values of the fractions, as well asthe lead susceptibility thereof.

Processing of the crude oil under the temperature and pressureconditions normally applied, frequently intensifies the undesirablecharacteristics noted. 'In catalytic cracking of petroleum fractionsthere is produced refractory recycle stock which is withdrawn from thesystem and includes a large proportion which falls in the household fuelor burning oil range. This is commonly referred to as light cycle oil orNo. 2 fuel oil. This material is found to be unstable in storage, losingcolor rapidly and developing gummy precipitates and possessing highlyundesirable odors, all of which make the product undesirable and often asource of mechanical difficulty in use.

Various processes are presently employed in an effort to render theseburning oil stocks satisfactory for their intended use. Among the moreextensively used processes is hydrogenation which necessarily involvesexpensive equipment and high operating costs. Another process used isthe treatment of the oil with concentrated caustic soda solutionfollowed by subjecting the alkali treated oil to the action ofelectrical precipitators in order to remove, to the greatest extentpossible, traces of the alkali reaction products which would otherwiseremain suspended in the oil. This process, too, requires expensiveequipment and relatively high treating costs.

In my U.S. Patent No. 2,889,195, I have disclosed a comparatively simplechemical treatment by which the various petroleum distillates whichpossess the aforementioned undesirable characteristics may be renderedentirely free of these characteristics.

In the patented process, I employ as the chemical reagents, an organicacid anhydride, preferably acetic anhydride, and concentrated aqueousalkali hydroxide solution, preferably sodium hydroxide in aconcentration of at least 25% by weight of the alkali solution.

I have now discovered that by substituting sodium methylate for thealkali hydroxide as used in the patented process, I not only obtain thedesired results, so far as im- 3,384,575 Patented May 21, 1968 provingthe quality of the oil is concerned, but I am able to very markedlyreduce the quantity of chemicals required and the cost thereof. Byemploying sodium meth ylate, generally in a methanol solution, I havefound that the quantity of organic acid anhy-dride, as required in theearlier process, may be reduced by as much as or even more, and thequantity of sodium methylate required will be in the range of from about5% to 15% of the amount of caustic alkali previously required.

As in the case of the patented process, the process of the presentinvention may be applied to the various petroleum distillates atappropriate stages following their product-ion in conventional refiningoperations, or may be applied to the crude petroleum itself prior tosubjecting it to the usual processing operations. In the case of thecatalytically cracked cycle stocks, the process will usually be appliedto the cycle stock in order to obviate the undesirable propertiesimparted to this material by the catalytic treatment.

The process in accordance with this invention comprises the liquid phasechemical treatment of petroleum by two reagents applied to the oil insuccession under controlled conditions.

In accordance with the preferred embodiment of this invention, the firsttreatment stage comprises, thoroughly admixing with the oil a smallproportion of acetic anhydride and thereafter, without intermediatesettling or other processing, the second stage comprises vigorouslyadmixing with the oil containing the acetic anhydride, a small quantityof sodium methylate (sodium methoxide), preferably in a methanolsolution. Because of the relatively minute amounts of chemicals requiredto complete the reactions involved, the reaction products usually willbe so small in quantity that they may be permitted to remain in thetreated oil without any deleterious effect.

As indicated previously, it is one of the unexpected results of thesubstitution of sodium methylate for aqueous alkali solutions of thepatented method, that the total quantity of reagents, including the acidanhydride, is reduced to such a small quantity, both relatively and inabsolute terms, that no separating step for reaction products willordinarily be required, and it is further found that the reactionproducts, whatever their character, when left in the oil, do not, asnoted previously, have any adverse effect on the stability of the oil.

It is found that treatment of the oil by the process described, removesundesirable .od'ors; renders the oil completely stable to the standardstability test (which comp-rises subjecting a sample of the oil in anopen container to a temperature of 212 F. for 24 hours), the resultingstability obviating color loss or formation of precipitates. In manyinstances, the oil will be rendered sweet to the conventional doctortest.

In the case of gasoline distillates, the treatment frequently results inimprovement in the clear octane values of such stocks, as Well asimproving the lead suscepti bility thereof.

The mechanisms of the reactions which occur in the treating process ofthe present invention is not fully understood, but it is thought thatsome type of acylation reaction occurs between the acetic anhydride (orother anhydride employed) and the mercaptans and other types of sulfurbodies in the oil, and with the nitrogenous bodies and phenolic or otherhydroxy or carboxylic com pounds which may be present. It will beunderstood, therefore, that this invention should not be considered asdependent upon any specific reaction mechanism or theory, but is to bebased upon the procedure employing certain specified reagents as hereinset forth.

As indicated previously, acetic anhydride is my preferred reagent forthefirst stage treatment, and sodium methylate, preferably in the form of a25% solution in methanol, for the second stage treatment.

Acetic anhydride is preferred because of its readily commercialavailability and comparatively low cost, although other acid anhydrides,both aliphatic and aromatic may be used, but are generally moreexpensive and not as efficient, in some instances, as the preferredacetic anhydride. Other anhydrides include propionic, butyric andhexanoic anhydrides in the aliphatic category, and phthalic and benzoicanhydrides in the aromatic category. The latter, being normally solids,must first be dissolved in a suitable solvent, such as benzol, whichwill be fully miscible with the oil being treated. Mixtures of theanhydrides can also be used.

The entire procedure in accordance with this invention is a liquid phasetreating process which is normally conducted at atmospheric temperaturesand pressures, although where lig ht gasoline distillates are treated,the ope-ration may be conducted in a closed system under sufficientpressure to prevent vaporization and loss of light fractions.

The anhydride, preferably acetic anhydride, is added to the oil inproportions varying generally with the charactor and source of the oilbeing treated. In general, only a very small amount of acetic anhydrideis necessary, this amount being in the range from about 0.001% by volumeto about 0.005% by volume of the oil being treated. In the case of lightcycle oil from catalytic cracking, generally from about 0.002. to 0.005%by volume of acetic anhydride will be found to be most generallyapplicable. In the case of crude oil or other stocks having relativelylarge proportions of impurities, these quantities may be increased to 5to times the amounts heretofore stated.

The amount of the acetic anhydride and the time of contact with the oilmust be such that after subsequent treatment of the mixture of theacetic anhydride and oil with the sodium methylate solution, a sample ofthe treated oil heated in an oven at 212 for 24 hours shows an improvedcolor as compared to an untreated sample of the same oil heated at thesame temperature for the same time.

The sodium methylate solution is added to the admixture of the oil withthe acetic anhydride following the addition of the latter. The timeinterval between the additions to the oil of the first and secondreagents is variable, it being only important that the acetic anhydridebe thoroughly mixed with the oil before the sodium methylate solution isadmixed therewith. While ordinarily the sodium methylate Will be addedimmediately after cornpletion of the mixing of the acetic anhydride withthe oil, the treatment may be successfully effected even though thesodium methylate is added hours or days after the addition of the aceticanhydride to the oil.

It appears that whatever may be the reactions which occur between theacetic anhydride and the constituents of the oil, these reactions occursubstantially instantaneously so that it is only necessary to employsufiicient mixing to assure that the acetic anhydride has beenthoroughly distributed through the oil before the sodium methylatesolution is applied. 'It is important to note, therefore, that thereagents should be added separately and successively, the sodiummethylate solution following the anhydride addition, but that the timeinterval between the additions of the reagents is not particularlyimportant.

The quantities of sodium methylate added is quite small and is added inamounts generally sufiicient to neutralize any excess anhydride oracidic reaction products which may be formed, as calculated from theneutralization number of the oil as determined by the standard ASTM TestD-664-58. In general, the quantitles of sodium methylate required formost oil stocks will range from about 0.001% to about 0.05% by volume ofthe oil. For burning oils the quantities required 4 will be in the rangefrom about 0.005% to about 0.03% by volume of the oil.

As sodium methylate is a highly hygroscopic powder which will bedecomposed violently by water, it is ordinarily employed in a methanolsolution which may, of course, be varied in its concentration of sodiummethylate. As noted previously, a 25% solution of the reagent inmethanol is found generally preferable, but this concentration may bevaried if preferred. Since, as noted, the quantities of the reagents,particularly the sodium methylate solution, is extremely small, there isusually no necessity for any settling or separation of products of thereaction. Hence, the process may be termed a once-through process.

The time of treatment of the oil with the acetic anhydride should besufficiently long to assure adequate mixing and will vary somewhat,depending upon the volumes treated. Usually 15 seconds to 5 minutes willbe found adequate, but longer times may be employed. The subsequenttreatment with the sodium methylate solution is likewise dependentmainly upon the degree of agitation to be applied and as much time asmay be found necessary to assure complete and thorough mixing of thesodium methylate solution with the oil-anhydride mixture will berequired. This time may be of the order of a few seconds to severalminutes.

By way of comparison with the chemical requirements of the treatingprocess disclosed in my aforesaid US. Patent No. 2,889,195, thefollowing results were obtained in comparing the treatments, on acommercial scale on the order of 5,000 barrels per day, of a light cycleoil from catalytically cracked stock. Where the patented processrequired 0.03% by volume of the oil of acetic anhydride, the presentprocess required 0.0025% of acetic anhydride, and where the patentedmethod required 010% by volume of a 25 aqueous solution of sodiumhydroxide continuously circulated at a rate of about 5% by volume of theoil, the present method required the admixture with the oil-anhydridesolution of 0.005% by volume of a 25 methanol solution of sodiummethylate. In the case of both reagents, it will be seen that thevolumetric requirements were reduced by or more, and, of course, in thepresent process, no recirculation of the sodium methylate or separationof reaction products were required.

Following are some additional examples of treating various heating oilswith the present method:

EXAMPLE I A heating oil with an acid value of 0.03 mg. KOH/g., andhaving an initial union color of I /2+ when subjected to an acceleratedstorage stability test (vented storage at 212 1F. for 24 hours)deteriorated to 'an 8+ color. This oil was treated by dissolving in theoil 0.002% by volume acetic anhydride and then by vigorous agitating theoil with 0.011% by volume of sodium methylate (-25% solution inmethanol) a very small amount of insoluble reaction product was formedand separated from the oil. The separated oil had a storage stabilitycolor of 2-.

EXAMPLE 111 Another heating oil with an acid value of 0.01 mg. KOH/g.and an initial union color of 2- gave an accelerated storage stabilitycolor of 8+. This oil was treated with 0.0025% by volume of aceticanhydride followed by 0.03% by volume of sodium methylate (25 solutionin methanol) and after separation from the minute amounts of insolublereaction products which developed, produced an oil having storagestability color of 2 on the union colorimeter scale.

EXAMPLE 'III' Still another heating oil having an acid value of 0.02 mg.KOH/g., an initial union color of 1 /2+ and a union color of 5, after 24hours at 212 F. was treated with 0.0027% by volume of acetic anhydridefollowed by 0.0173% by volume of sodium methylate (25% solution inmethanol) and without separation of any precipitate, produced a treatedoil which maintained a lVz-I- union color on the storage stability test.

From the foregoing, it will be seen that the present invention providesan exceptionally effective, simple, low cost process for the treatmentof petroleum oils by which outstanding improvement in the physical andchemical properties thereof is effected. Distillate products such as thegasoline fractions and burning oil fractions, when treated by the methodin accordance with this invention, become finished stocks, requiring nofurther processing before use.

What I claim and desire to secure by Letters Patent is as follows 1. Themethod of refining petroleum oil, comprising, admixing with a petroleumoil stock in the liquid phase an organic acid anhydride selected fromthe group consisting of acetic, propionic, butyric, hexanoic, phthalicand benzoic anhydrides in an amount ranging from about 0.001% to about0.005% by volume of the oil stock, and thereafter agitating theadmixture with sodium methylate in an amount sufficient to neutralizesaid admixture.

2. The method of refining petroleum according to claim 1, wherein thequantity of sodium methylate added is in the range from about 0.001% toabout 0.05% by volume of the oil stock.

3. The method according to claim 1, wherein said petroleum oil stock isthe light cycle stock, commonly designated as No. 2 fuel oil, obtainedfrom the catalytic cracking of petroleum.

4. The method according to claim 1, wherein said organic acid anhydri-deis acetic anhydride.

References Cited UNITED STATES PATENTS 2,068,850 -1/'1937 Ellis 208-2822,769,766 11/1956 Folkins et al 208282 2,889,195 6/1959 Hoover 208-285FOREIGN PATENTS 401,353 12/1938 Germany.

DELBERT E. GANTZ, Primary Examiner.

GEORGE I. CRASANAKIS, Assistant Examiner.

